Method of stress relieving welded joints



Oct. 20, 1936. R C. NEWHOUSE 2,057,841

METHOD OF STRESS RELIEVING WELDED JOINTS Original Filed May 25, 1952 svW as; las am g g s Z xw l\| Ill m7////////////////////////////////////////////////////////// /Vvu im m ii 7E l 30 M0114 V 3/ i S s s M 2% I I I I /5 sbm\\\\\\\\\\wl\\\\\\\\\\\\\\\\\wt i Patented ct. 20, i936 METHOD FSTRESS RELIEVDYG WELDED JOINTS Original application May 23, 1932, SerialNo. 613,018. Divided and this application January 5, i935, Serial No.498

6 Claims.

This invention relates generally to the art of heat treating articlesand it relates more specifically to an improved method of stressrelieving Welded joints, an apparatus for carrying out the method beingclaimed in U. S. Patent 2,044,734, June 16, 1936, Ray C. Newhouse,Apparatus 'for stress relieving welded joints, the present applicationbeing a division of the application which has resulted in the grant ofsaid patent.

It is an object of the invention to provide an eicient and inexpensivemethod of stress relieving welded joints on metal structures of largedimensions.

Another object of the invention is to provide a method of stressrelieving welded joints on metal structures of large dimensions, whichmethod may be carried out without the employment of a furnace of largecapacity such as to receive and heat the entire metal structure.

Another object lof the invention is to provide a method of stressrelieving welded joints on metal structures of large dimensions, whichmethod may readily be carried out at the place where the metal structureis to be erected or assembled, that is, outside of its place ofmanufacture.

A` more specific object of the invention is to provide an eflicient andinexpensive method of stress relieving Welded joints on plate metalvessels and other plate metal structures of large dimensions, such ascylindrical shells for grinding mills, kilns, and other machines,boilers, penstocks `and the like.

These and other objects and advantages of the invention will be apparentfrom the following 35 description. A clear conception of a preferredmanner in which the method.according to the invention may be carriedout, may be had by referring to the drawing accompanying and forming apart of this specification, in which like reference characters designatethe same or simi-' lar parts in the several views.

Fig. 1 is a vertical longitudinal section through a cylindrical shell ofa rotary kiln or the like, with an apparatus for stress relieving acircum- 0- ferential joint applied thereto.

r 4 Fig. 2-is an enlarged section on line II-II of Fig. 1.

Fig. 3 is anenlarged section on line III- HI of Fig. 2. v

Fig. 4 is a vertical transverse section through a furnace of modifiedconstruction for stress relieving longitudinal joints.

'Ihe numeral l indicates generally the 'cylindrical shell of a rotarykiln or like structure Y', which is made in sections, each sectionconsisting of a steel plate 2 rolled into cylindrical shape and havingits ends connected together by a longitudinal welded joint 3. Adjoiningsections of the cylindrical shell are connected together by weldedcircumferential joints A. A portion of 5 the shell l, where acircumferential joint occurs,

is surrounded exteriorly by a ring shaped casing comprising six sections5; and another ring shaped casing comprising six sections 6 is placed,concentric with the outer casing, interiorly of 10 the shell so as tocover the welded joint and the adjacent portions of the cylindricalshell sections between which the welded joint occurs.

Each section 5 of the outer casing has a curved top wall and side wallsspaced in the direction of the axis of the shell and extending in planesat right angles thereto. The top wall is formed of a sheet metal facing'l and a lining 8 of heat insulating material, such as asbestos. Theside walls are constructed similarly of sheet metal facings 9 and l0 andlinings ll and l2 of heat insulating material. The sheet metal facingsof the top and side walls are secured together, as by welding, and theyform a frame, so to speak, for supporting the heat insulating materialwhich is secured thereto. Sheet metal members i3 and I4 somewhat similarto the sheet metal facings 9 and I0 of the side walls are secured to theinner surface of the sheet metal facing l, for instance by welding, andlinings l5 and i6 of heat insulating material are secured thereto in anysuitable manner. The sheet metal members I3 andi Hl and the heatinsulating linings i5 and I6 secured thereto do not extend down to thesurface of the cylindrical shell. They are intended to serve as bafflesdividing the interior space of each ring section into a central zoneadjacent to the welded joint and lateral zones in communication with thecentral zone. Arranged in the central zone and supported by the top wallof the casing section 5 are four heating elements in the form ofelectric resistance coils l1 from which heat is transmitted to thewelded joint by radiation. The ends of the coils ll are clamped toterminal studs i8 carried by the ring sections, the terminal studsprojecting through the top wall of the ring section in order tofacilitate the making of electrical connections.

Secured to the sheet metal facing 1 of each ring section 5 are anges i9,one at each end of the section, which ilanges permit adjacent ringsections to be rigidly secured together. Similar flanges 20 are securedto the sheet metal facings 9 and Ill of the side walls. The flanges aresuitably drilled for receiving through bolts which may hold the sectionssecurely together. When all six ring sections of the outer casing aresecurely clamped together by means of their anges i9 and 20, a rigidring shaped structure of a given inside diameter is obtained, saidinside diameter being determined by the distance between diametricallyopposed points on the inner edge of the ring formed by the circularlyarranged side walls 9 or I0 of the casing sections 5. This insidediameter of the outer casing is preferably somewhat larger than theoutside diameter of the cylindrical shell to which the casing is'to beapplied, and spacers 2i and 22 of heat insulating material are providedto lill the the gaps between the outer surface of the cylindrical shelland the side walls of the casing sec-A tions 5. By means of the spacersan outer ring shaped casing of fixed inside diameter may be accommodatedto cylindrical shells of different diameters as the thickness of thespacers may vary to a considerable extent. Thus, for instance, if theoutside diameter of the shell is only slightly less than the insidediameter of the casing, spacers of less thickness than that shown -inthe drawing may be used, and if the outside diameter of the shell andthe inside diameter of the casing differ considerably, correspondinglythicker spacers may be used. The spacers are valuable also in that theyprevent contact between the shell and the metal facing o f the casingsections which contact may tend to produce an undesirable dissipation ofheat from the shell. When the outer casing sections are assembled asshown in Fig. 2, the terminal studs I8 of the heating coils Ill may beconnected by straps 23 in any desired combination. 2li indicates 'theconnections of the heating coils il with a source of electrical energynot shown.

The inner casing which consists of the six sections 6 is constructed ina similar manner as the outer casing. Each section 6 has a curved bottomwall and side walls, the bottom wall coniprising' a sheet metal facing2l and a lining 219" of heat insulating material, and the side wallscomprising sheet metal facings 29 and 39, and linings 3l and 32. Bales,corresponding to the baffles of the outer casing sections, are formed bysheet metal members 33 and 36 and liningsV 35 and. Arranged in thecentral zone of each inner casing section 6 and supported by the bottomwall thereof are four heating elements in the form of electricresistance coils 3l from which heat is transmitted to the Welded jointby radiation. The ends of the coils are clamped to terminal studs 38projecting through the bottom wall of the inner casing section 6 inorder to facilitate the making of electrical connections.

The inner casing sections 6 are clamped together by means of anges 39and 40 and through bolts in a similar manner as the outer casingsections 5, and when assembled form a rigid structure of a given outsidediameter, the latter being determined by the distance betweendiametrically opposed points on the outer edge of the ring formed by thecircularly arranged side walls 29 or 30 of the casing sections 6. 'I'hisoutside diameter of the inner casing is preferably somewhat smaller thanthe inside diameter oi the cylindrical shell to which the casing is tobe applied, and spacers 4| and 42 of heat insulating material areprovided to fill the gaps between the inner surface of the cylindrical-shell and the side walls of the casing sections 6. By using spacers ofdiiferent thickness an inner ring shaped casing of given outsidediameter may be accommodated to cylindrical shells of differentdiameters as explained in connection with the outer casing. 25 and 26indicate straps and electrical connections similar to the straps 23 andelectrical connections 2t mentioned in connection withthe outer casing.

A circumferential welded joint of the cylindrical shell i may be stressrelieved by means of the apparatus described hereinbefore, as follows.The inner and outer ring shaped casings are applied to the shell asshown in the drawing, that is, the outer ring shaped casing is broughtinto such position that the central zone with the heating elements isdirectly above the joint, and similarly, the inner casing is broughtinto such position that the open side of the central zone with theheating elements faces the joint. In these positions the casings form,as will be seen. heat retaining hoods over the welded joint and theadjacent portions of the cylindrical shell sections which arecircumferentially connected by the joint. For purposes of description itmay be assumed that the heating coils of the individual casing sectionsare connected as shown in Fig. 2, that is, that the heating coils Il ofthe outer casing sections are connected in series by the straps 23 so asto forma circuit terminating in the connections 2t, and that the heatingcoils 3l of the inner casing sections 6 are likewise connected in seriesby the straps 25 so as to form a circuit terminating in the connections26. The connections 26 and 2S lead, as stated, to a suitable source ofelectric energy, and it should be understood that such energy will becaused to ow simultaneously through the two circuits formed by theheating coils il and 3i'. As a result, heat will be generated at thejoint interiorly and exteriorly of the shell and sub.- stantiallythroughout the length of the joint, circumferentially of the shell, aslong as there is a ilow of electric energy through the two circuits.

Upon connecting the two circuits to the source of energy the portions ofthev shell covered by the inner and Outer casings will be caused to warmup, and due to the substantially uniform distribution of the heatlongitudinallyof the joint, there will be a substantially uniform riseof temperature in the shell longitudinally pi the joint and throughoutthe length of the latter. Suicient energy will be supplied by the sourceto the two circuits to develop the amount of haat which is necessary toeffect complete relieving of stresses in the joint and in the adjacentportions of the shell in Which'stresses, due to the welding, are likelyto exist, the procedure/in this connection being governed by the sameprinci ples which have heretofore been followed in the operation of,stress-relieving furnaces of well known construction which' weredesigned to receive the whole structure on which a welded joint was tobe stress relieved. As distinguished from this well known operation,however, the stress relieving operation by means of the apparatusdisclosed herein does not contemplate heating the entire structure to astress relieving temperature but only that part thereof in whichstresses, due to welding, are likely to exist. The well known methodreferred to is often impractical where the structure on which the weldedjoint occurs is large; the rotary kiln shell mentioned above being anexample, and pipe sections for hydraulic power plants, such as theBoulder Dam project now under construction, in which pipe sections ofthirty feet diameter are used, being another. Furnaces large enough sothat such structures could be placed into them would be too expensive tobuild and would also be expensive to operate considering that, accordingto established practice, it is considered necessary to bring thestructure slowly up to the comparatively high temperature, usually wellabove l000 F., required to effect the relieving of stresses, and to holdit at that temperature for a period of at least one hour per inch ofthickness. The apparatus disclosed herein may be built at cornparativelylow costs'tot the largest structures, and the costs for operating it inthe manner of th'e well known furnaces, that is, so as to effect a slowrise of temperature and to hold the temperature at the specified heightfor the required length of time, would likewise be comparatively low.The results accomplished, however, would be equivalent to thoseaccomplished with the well known furnaces in that the temperature of thejoint and of the adjacent portions of the structure are raised uniformlythroughout the length of the joint, until the temperature required forthe relieving of stresses has been reached, said temperature being thenalso uniform longitudinally of the joint and throughout the length ofthe joint. After said temperature condition has been maintained for therequired length of time, the joint and the adjacent portions of thestructure, as in the well known furnaces, are allowed to cool slowly ina still atmosphere, the heat insulating casings remaining applied duringthe cooling period. After the temperature of the joint and the adjacentportions of the shell has sunk below the minimum temperature permittingthe relieving of stresses and to a temperature at which it is safe toexpose the covered portions of the structure to the open air, thecasings may be removed.

It should be noted that the heat insulating linings l and IB restrictthe transmission of heat from the heating coils l1 into the lateralcompartments of the outer casing, and that the heat insulating linings35 and 36 likewise restrict the emission of heat from the heating coils31 into the lateral compartments of the inner casing. The portions ofthe shell in which stresses, set up during the welding of the joint, mayexist lie between the baffles, and these are so'spaced, transversely ofthe joint, that the widths of the central compartments of the casingsare ample to accommodate those portions of the' shell. In other words, aplane through the heat insulating linings l5 and 35, at the sidesthereof facing the heating coils, and a plane through the heatinsulating linings i6 and 36,' at the sides thereof facing the heatingcoils, are spaced from each other transversely of the joint, for adistance substantially equal to the width of the portion of the shell,in which stresses are to be relieved. The lateral compartments of thecasings 5 and are of substantial widths, transversely of the joint, andthere are two zones on the shell, one between the bailies l5 and 35, andthe other between the baffles i6 and 36, where the shell portion coveredby the central compartments of the casings 5 and 6 merges with the shellportions covered by the lateral compartments of the casings 5 and 6. Itis desirable that there be no sudden drop of temperature, transverselyof the joint, in these merging zones and in this connection thefollowing should be noted.v l The spacing of the free ends of the heatinsulating linings l5 and i6 from the outer surface of the shell, andthe spacing of the free ends of the heat insulating linings 35 and 36from the inner surface of the shell have the effect that, when theportion of the shell within the central compartment is brought up to asuitable stress relieving temperature, a certain amount of heat may passfrom the central compartment into the lateral compartments, and whilethe portion of the shell in the central compartment is kept at stressrelieving temperatures, the shell portions of the merging zones and theportions of the shell in the lateral compartments will be attemperatures gradually decreasing transversely of the joint. Any othersuitable means for obtaining this effect or for making it more or lesspronounced, may be used. The object aimed at is to avoid the arising ofany harmful conditions vin the portions of the shell adjacent to theportion from which stresses are to be relieved. In this connection itshould be noted that, while the temperature of the shell portions withinthe lateral compartments of the casings is of gradually decreasingheight transversely of thejoint, the temperature distribution in theseportions is substantially uniform circumferentially of the shell, thatis, longitudinally of the joint, and that such circumferentially uniformand transversely decreasing temperature distribution will exist whilethe temperature of the shell portions Within the central compartments ofthe casings is substantially uniform circumferentially of the shell aswell as transversely of the joint. During cooling, while the casingsremain applied to the shell, the emission of heat from the portions ofthe shell within the casings is restricted, and the cooling of theseportions will, therefore, be uniform circumferentially of the shellthroughout the length of the joint.

The means for generating heat are here shown in the form of electricheating coils, but different means for heating the joint uniformlythroughout its length may be employed. Instead of velectric heating byradiation, as shown in the drawing, electric heating by induction (highfrequency current) may be used. If it should be desired to heat bycombustion the construction of the casings may be modified accordinglyin order to provide an adequate supply of oxygen but still prevent a toorapid dissipation of heat during the cooling period.

It should also be noted that the construction of the casings insections, particularly of the inner casing, offers advantages. Forinstance, if it is desired to stress relieve circumferential joints in avessel which is closed at both ends, the sections of the inner casingmay be brought into the vessel through a manhole or the like, assembledwithin the casing, and removed again after disassembly.

A modified construction of the apparatus described hereinbefore, whichis suitable for stress relieving longitudinal joints of a cylindricalplate metal structure, is shown in Fig. 4. The apparatus is constructedon the same principles as explained in connection with Figs. 1 to 3. Itconsists of an outer casing 43 and an inner casing dll, the interiorspace of each casing being divided by baffles d5 into a central zone,enclosing heating elements 86, and lateral zones intended to cover theportions of the plate metal structure adjacent to the joint, and tocause a gradual decrease of temperature from the heated joint to saidadjacent portions. Spacing blocks 41 of heat insulating material areused for purposes of adjustment and for preventing metallic contactbetween the surface of the cylindrical structure and the side walls ofthe casings. Fig. 1 shows in dash-dotted lines the' application of afurnace according to Fig. 4 to the longitudinal joint of a section ofthe cylindrical shell i. It should be understood, however, that thelongitudinal joints of a structure like the cylindrical shell l arepreferably stress relieved before the sections are joined together bycircumferential joints.

The furnace shown in Fig. 4 may also be modied for application to awelded joint between straight metal plates, in which case the outer andinner casings 43 and 44 would preferably take the form of square boxeshaving each one open side facing the plate metal.

It should be understood that it is not intended to limit the inventionto the exact details of construction and procedure herein shown anddescribed, for various modifications within the scope of the claims mayoccur to persons skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. The method of relieving a zone of a metal structure from stresses dueto a welded joint in said zone, which includes the step of heatingthemetal of said zone to a stress relieving temperature which is uniformthroughout the length and width of said zone, and the step of applyingto portions of said structure, adjacent to said zone, while saidadjacent portions are subject to heating by dissipation of heat fromsaid zone, additional heat of such intensity as to create in saidadjacent portions wide zones laterally of said first zone, wherein thetemperature decreases substantially continuously transversely of saidjoint and wherein the temperatures are uniform longitudinally of saidjoint.

2. The method of relieving a zone of a metal structure from stresses dueto a welded joint in said zone, which includes the step of heating themetal of said entire zone simultaneously throughout the width and lengthof said zone to a substantially uniform stress relieving temperature,and the simultaneous step of applying to portions of said structureadjacent to said zone and subject to heating by `dissipation of heatfrom said zone, additional heat simultaneously throughout the lengths ofsaid adjacent portions longitudinally of said joint, said additionalheat being of suicient intensity and graded transversely of said jointso as to create in said adjacent portions Wide zones laterally of saidfirst zone, wherein the temperature decreases substantially continuouslytransversely of said joint and wherein the temperatures are uniformlongitudinally of said joint.

3. The method of relieving a zone of a metal structure from stresses dueto a welded joint in said zone, which includes the step of heating the-metal of said entire zone simultaneously throughout the width andlength of said zone to a substantially uniform stress relievingtemperature, and the step of applying to portions of said structureadjacent to said zone, while said adjacent portions are subject toheating by dissipation of heat from said zone, additional heat ofsuicient intensity and graded transversely of said joint so said joint.

as to create in said adjacent portions wide zones laterally of saidfirst zone, wherein the temperature decreases substantially continuouslytransversely of said joint and wherein the temperatures" are uniformlongitudinally of said joint.

4. The method of relieving a zone of a metal structure from stresses dueto a welded joint in said zone, which includes the step of heating themetal of said zone to a stress relieving temperature which is uniformthroughout the length and width of said zone, and the step of applyingto portions of said structure adjacent to said zone, while said adjacentportions are subject to heating by dissipation of heat from said zone,additional heat simultaneously throughout the lengths of -said adjacentportions longitudinally of said joint, said additional heat being ofsuflicient in-l tensity and graded transversely of said joint so astocreate in said adjacent portions wide zones laterally of said rst zone,wherein the temperature decreases substantially continuouslytransversely of said joint and wherein the temperatures are uniformlongitudinally of said joint.

5. The method of relieving a zone of a plate metal structure fromstresses due toa Welded joint in said zone, which includes the step ofheating the plate metal of said entire zone simultaneously from oppositesides thereof to a stress relieving temperature which is uniformthroughout the length and width of said zone, and the step of applyingto portions of said structure adjacent to said zone, while said adjacentportions are subject to heating by dissipation of heat from said zone,additional heat simultaneously from opposite sides of said adjacentportions, saidadditional heat being of sufficient intensity and gradedtransversely of said joint so as to create in said adjacent portionswide zones laterally of said first,

zone, wherein the temperature decreases substantially continuouslytransversely of said joint and wherein the temperatures are uniformlongitudinally of said joint.

6. The method of relieving a zone of a plate of heat from -said zone,additional heat of such intensity as to create in said adjacent portionswide zones laterally of said first zone, wherein the tov temperaturevdecreases substantially continuously transversely of said joint andwherein the temperatures are uniform longitudinally of said joint;maintaining said uniform temperature distribution in said rst zone andsaid longitudinally uniform and transversely decreasing temperaturedistribution in saidlateral zones for a suicientf length of time toeffect complete relieving of stresses in said rst zone, and lowering thetemperatures in said first and lateral zones unifornly throughout thelengths thereof longitudinally of'l RAY C. NEWHOUSE:

